基于JMatPro热力学软件计算并考虑化学元素间相互影响，设计了690 MPa级抗震耐蚀防火功能结构一体化高强建筑用钢，其化学成分(质量分数，%)主要为：Fe-0.08C-0.3Si-1.1Mn-0.12(Nb + V + Ti)-1.6(Cr + Cu +Ni + Mo)-0.002B-0.004N。经实验室冶炼和控轧控冷工艺(TMCP)处理后，采用EPMA、EBSD等多种微观分析和性能测试手段对该低碳微合金钢的微观组织特征、强韧化机理和力学性能、防火性及耐蚀性等进行了表征和分析。结果表明，所设计的低碳微合金钢TMCP状态下的微观组织包含粒状贝氏体、板条贝氏体和贝氏体铁素体；室温下屈服强度达700 MPa，抗拉强度为878 MPa，屈强比为0.80，断后延伸率为20%，并具有良好的低温韧性。低碳微合金钢在600℃保温1~3 h时，均达到耐火性能要求；并对其在海洋环境下的耐蚀性进行了评价，发现粒状贝氏体对耐腐蚀性能具有积极作用。进一步分析表明，低碳微合金钢具有良好的强韧性源于析出强化、细晶强化、位错强化和固溶强化的综合作用；对低温冲击断口截面组织分析表明，裂纹会多次穿过板条贝氏体呈“Z”字型扩展以消耗更多的能量，也是该钢具有良好低温韧性的原因。

The rapid development of high-rise buildings has increasingly brought requirements for construction steels with high strength and toughness. For high-rise building structural steels with low yield ratio, good weldability and excellent resistance to fire and corrosion are generally required. However, high grade construction steels with comprehensive properties are yet to be developed. In this study, a 690 MPa grade functionally structured fire and corrosion resistant high strength construction steel was designed based on the thermodynamic calculations of the JMatPro software and interactions among chemical elements. The chemical composition (mass fraction, %) of the designed steel was Fe-0.08C-0.3Si-1.1Mn-0.12(Nb + V + Ti)-1.6(Cr + Cu + Ni + Mo)-0.002B-0.004N. After laboratory melting and a thermomechanical controlled process (TMCP), the microstructure features, strengthening and toughening mechanisms, mechanical properties, and fire and corrosion resistances were characterized and analyzed by EPMA, EBSD, and performance testing. Results show that the microstructure of this low-carbon microalloyed steel at its TMCP state is mainly composed of bainite ferrite, granular bainite, and lath-like bainite. The yield strength, tensile strength, total elongation, and yield ratio at room temperature are 700 MPa, 878 MPa, 20%, and 0.80, respectively, and this steel possesses good low-temperature toughness. This low-carbon microalloyed steel meets requirements for fire resistance at elevated temperatures up to 600^oC for 3 h. It is disclosed that the granular bainite plays a positive role in improving corrosion resistance under marine environment. A further analysis shows that the tested steel possesses excellent strength and toughness resulting from the cumulative effects of precipitation strengthening, grain refinement strengthening, dislocation strengthening, and solid solution strengthening. Moreover, after observation and analysis of crack initiation and propagation underneath the fractured surface of low-temperature impacted samples, the microvoids prefer to nucleate at high-angle boundaries containing brittle phases and grow in a Z-type to cross lath-like bainite to consume more energy. Multiple crack deflections are beneficial for toughness improvements.